This invention relates to telecommunications and, more particularly, to acknowledgement by a receiving side to a transmitting side of receipt of a message over a communications link.
A transmitting side communicating with a receiving side over a communications link will often require acknowledgement of messages and therefore provide for an xe2x80x9cacknowledge modexe2x80x9d. Messages, for instance, packets, signaling sequences, or the like are identified to the receiving side as requiring acknowledgement. An acknowledgement in the form of one or more bits of a signaling sequence, packet or the like in the reverse direction from the receiving side to the transmitting side indicates receipt of the message. Provision may also be made for positively indicating, one way or the other, whether the message was received correctly or not. The transmitting side waits for the acknowledgement message and takes further steps contingent upon receipt or non-receipt thereof. Similarly, an xe2x80x9cunacknowledge modexe2x80x9d can be defined for such communications links, wherein for a given sequence of messages it is negotiated by signaling between the transmitting and receiving sides that such messages are not to be acknowledged. For instance, important data messages might use the xe2x80x9cacknowledge modexe2x80x9d, while other types of messages, such as voice, might not, and instead use the xe2x80x9cunacknowledge modexe2x80x9d.
With certain types of applications some of the transmitted protocol data units are more important than others to be received correctly. Thus, acknowledgements are needed to get the information whether important packets were lost or not, while acknowledging unimportant packets would simply increase delay, waste capacity and decrease throughput.
Unfortunately, both the known xe2x80x9cacknowledge modexe2x80x9d and xe2x80x9cunacknowledge modexe2x80x9d require that all messages, packets, or the like be either acknowledged or not acknowledged.
The object of the present invention is to provide a selective acknowledgement scheme for a wireless interface between a transmitting side and a receiving side.
According to the first aspect of the present invention, a method for use in a telecommunications system having the capability to exchange information packets over a communications link in both an acknowledge mode in which reception by a receiver of all information packets transmitted by a transmitter over the communications link are acknowledged by the receiver sending at least one acknowledge message over the communications link back to the transmitter and in an unacknowledge mode in which none of the information packets transmitted by the transmitter over the communications link are acknowledged by the receiver, is characterized by said transmitter in said unacknowledge mode nevertheless determining from among a plurality of packets destined for transmission to the receiver in said unacknowledge mode a selected packet for which an acknowledgement of receipt from the receiver is required, and signaling said receiver that said acknowledgement of receipt of said selected packet is required from the receiver.
In further accord with to the first aspect of the invention, said transmitter after transmitting said selected packet, waits during a set time period thereafter for receipt of said acknowledgement from said receiver before taking further steps contingent on said acknowledgement of receipt by said receiver.
Still according to the first aspect of the invention, said transmitter stores the selected packet during said set time period at least until said receipt of said acknowledgement from said receiver.
Still further according to the first aspect of the invention, said transmitter, after said selected packet is transmitted to the receiver, also stores during said set time period packets for which acknowledgement is not required at least until said receipt of said acknowledgement from said receiver.
According still further to the first aspect of the invention, said transmitter retransmits to said receiver said stored selected packet and said stored packets for which acknowledgement was not required after said set time elapses without receipt of said acknowledgement from said receiver.
Further still according to the first aspect of the invention, said transmitter retransmits to said receiver said stored selected packet after said set time elapses without receipt of said acknowledgement from said receiver.
In further accordance with the first aspect of the invention, the transmitter receives over said communications link from said receiver an acknowledgement of receipt of said selected packet and notifies a higher layer in a protocol stack of the transmitter of said receipt of said selected packet by said receiver.
Yet further still according to the first aspect of the invention, said transmitter waits for at least one further set time period after said step of retransmitting said stored selected packet for an acknowledgement of receipt thereof from the receiver before finally concluding that said retransmitted stored selected packet was not received by the receiver.
According further to the first aspect of the invention, said transmitter waits for at least one further set time period after said step of retransmitting said stored selected packet and said stored packets for which acknowledgement was not required, for an acknowledgement of receipt of the stored selected packet from the receiver before finally concluding that said retransmitted stored selected packet was not received by the receiver.
According still further to the first aspect of the invention, said transmitter concludes after lapse of said set time period without receiving said acknowledgement that said selected packet was not received by said receiver.
According yet further to the first aspect of the invention, said receiver in said unacknowledge mode determines reception over said communications link of said selected packet for which acknowledgement of receipt is required, and signals said acknowledgement of receipt to said transmitter over said communications link.
Further still according to the first aspect of the invention, said receiver determines whether said received selected packet was received correctly or not wherein said step of signaling said acknowledgement of receipt to said transmitter indicates correct or incorrect reception.
Yet still further according to the first aspect of the invention, said transmitter stores the selected packet during said set time period at least until receipt of said acknowledgement from said receiver and upon receipt by said transmitter of said acknowledgement indicative of incorrect reception of said selected packet, retransmits said selected packet.
Still further according to the first aspect of the invention, said receiver, after determining the selected packet was received incorrectly, continues to process incoming packets without any change in processing method therefor.
Yet further still according to the first aspect of the invention, said receiver saves packets received after determining the selected packet was received incorrectly until receiving the selected packet correctly after which the receiver processes incoming packets according to a method identified by said selected packet.
Still in accordance with the first aspect of the invention, the transmitter receives over said communications link from said receiver an acknowledgement of receipt of said selected packet and by notifying a higher layer in a protocol stack of the transmitter of said receipt of said selected packet by said receiver.
According to a second aspect of the invention, a transceiver having a receiving section and a transmitting section for use on both a receiving side and a transmitting side in a telecommunications system having the capability to exchange information packets over a communications link in both an acknowledge mode in which reception by a receiver section of a transceiver on the receiving side of all information packets transmitted by the transmitter section of a transceiver on the transmitting side over the communications link are acknowledged by the receiver section sending at least one acknowledge message over the communications link back to the transmitter section and in an unacknowledge mode in which none of the information packets transmitted by the transmitter section over the communications link are acknowledged by the receiver section, is characterized by said transmitter section in said unacknowledge mode nevertheless having means for determining from among a plurality of packets destined for transmission to the receiver section in said unacknowledge mode a selected packet for which an acknowledgement of receipt from the receiver section is required, and means for transmitting a signal to said receiver section that said acknowledgement of receipt of said selected packet is required from the receiver section.
According further to the second aspect of the invention, said transmitter section receives over said communications link from said receiving side an acknowledgement of receipt of said selected packet and by notifying a higher layer in a protocol stack of the transceiver of said receipt of said selected packet by said receiving side.
Further according to the second aspect of the invention, the transceiver is further characterized by said transmitter section having means for waiting during a set time period after transmitting said selected packet for receipt of said acknowledgement from said receiver section before taking further steps contingent on said acknowledgement of receipt by said receiver section.
Still further according to the second aspect of the invention, the transceiver is further characterized by said transmitter section having means for storing the selected packet during said set time period at least until said receipt of said acknowledgement from said receiver section.
Yet still further according to the second aspect of the invention, the transceiver is further characterized by said transmitter having means for also storing, after said selected packet is transmitted to the receiver, during said set time period packets for which acknowledgement is not required at least until said receipt of said acknowledgement from said receiver.
Yet further according to the second aspect of the invention, the transceiver is further characterized by said transmitter having means for retransmitting to said receiver said stored selected packet and said stored packets for which acknowledgement was not required after said set time elapses without receipt of said acknowledgement from said receiver.
Further in accordance with the second aspect of the invention, the transceiver is further characterized by said transmitter having means for retransmitting to said receiver said stored selected packet after said set time elapses without receipt of said acknowledgement from said receiver.
Further according to the second aspect of the invention, the transceiver is characterized by said transmitter section receiving over said communications link from said receiving side an acknowledgement of receipt of said stored selected packet and by notifying a higher layer in a protocol stack of the transceiver of said receipt.
Yet further in accordance with the second aspect of the invention, the transceiver is characterized by said receiver section in said unacknowledge mode having means for determining reception over said communications link of said selected packet for which acknowledgement of receipt is required, and means for signaling said acknowledgement of receipt to said transmitter second over said communications link.
Still further in accordance with the second aspect of the invention, the transceiver is characterized by said receiver section determining whether said received selected packet was received correctly or not, wherein said step of signaling said acknowledgement of receipt to said transmitter section indicates correct or incorrect reception.
Further still in accordance with the second aspect of the invention, the transceiver is characterized by said transmitter section storing the selected packet during said set time period at least until receipt of said acknowledgement from said receiver section and upon receipt by said transmitter section of said acknowledgement indicative of incorrect reception of said selected packet, retransmitting said selected packet.
Yet still in accordance with the second aspect of the invention, the transceiver is characterized by said receiver section, after determining the selected packet was received incorrectly, continuing to process incoming packets without any change in the processing method therefor.
Further in accordance with the second aspect of the invention, the transceiver is characterized by said receiver section saving packets received after determining the selected packet was received incorrectly until receiving the selected packet correctly after which the receiver section processes incoming packets according to a method identified by said selected packet.
This invention proposes a selective acknowledgement scheme that could be used for guaranteeing that important information is correctly received. The acknowledgement concept itself is a well-known technique to ensure that the data is correctly received. In this case, the data can be transmitted in unacknowledged, i.e., unreliable mode but higher layers of the protocol stack can ask for specific acknowledgements for certain packets. For instance, RTP/UDP/IP header compression could be used as an example application (acknowledgement of reference packets, reference time stamp of sequence number).
The invention as applied to header compression works as follows:
when the compression function wants to transmit reference values to the decompressor, it gives the data to the lower protocol layer with information that this packet needs to be acknowledged. The information that acknowledgement is needed can be carried in the protocol header or transferred by some other means, such as a specially defined primitive. When the decompressor acknowledges the packet, the information is given back to the higher protocol layer via the header or special primitive and directed to the certain function, e.g., the header compressor, which can now be sure that the particular packet (reference point) is correctly received. If the acknowledgement is not received within a predefined time, the compressor resends the reference point.
The description below assumes a General Packet Radio Service (GPRS) protocol stack. The application is as well applicable to any other telecommunications system.
Also, the GPRS protocol stack may evolve so that, e.g., SNDCP or LLC layers are removed. That does not change the applicability of the invention. The method may be applied also for other links/protocols than radio interface, e.g., BSSCP used in Gb interface between SGSN and BSS, Abis over satellite link.
The invention suits very well the situation where part of the packets are more important than others. Acknowledgement schemes have been specified to UMTS and to EGPRS. Thus only relatively small modifications to those schemes are needed.
The main application presently in mind for this invention is RTP/UDP/IP or TCP/IP header compression over a wireless link. Efficient header compression relies not on transmitting whole header fields but rather changes compared to some reference field or packet. If the reference packet was not received correctly the decompressor loses the compressor state and many packets will be lost before a new reference is correctly received. For this reason, an acknowledgement scheme is needed for these reference packets. The present invention solves this problem without wasting capacity/increasing delay by acknowledging normal packets.
Another important application of the present invention is different types of image and video coding schemes used in various telecommunications systems. Coding is often based on using some frame or lower-resolution image as a reference point to deduce the next frame of full-resolution image. As in the case of header compression, it is important that the reference point is correct. Thus, the invention could be utilized by having certain important frames acknowledged while less important frames (e.g., smaller details of a picture) can be sent without acknowledgements.
These and other objects, features and advantages of the present invention will become more apparent in light of the detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings.